During earth drilling air may be utilized as a drilling fluid. Along with air injected into the drilling apparatus, water may be introduced to suppress dust generated during the drilling. There may be a desire to separate the flow of air and water. One reason for this is that the water may be acidic. As a result, the water may have a corrosive effect on the bearings utilized in a drill bit. This can shorten the life of the bearings and, hence, the drill bit, requiring replacement of the bit. Of course, when the bit needs to be replaced the drill is not being utilized, this costs time and money to replace the bit and also takes a drilling rig out of productive use. It is desirable to remove as much water as possible from the flow of air to bearings, while directing the remaining air and separated water flow to the nozzles of the bit.
A typical apparatus utilized to separate air and water may utilize centrifugal force to separate the water from the air by directing the water away from inlets of bearings of a bit. One apparatus utilizing centrifugal force may include a plurality of vanes 1 including flat blades, shown in FIGS. 1A and 1B. A dome 3 may be arranged in the center of the vane assembly. Inlets 5 for air-tubes 7 to direct air toward bearings of the bit are arranged about one inch below the dome 3, as shown in FIG. 2B. The vanes 1 cause the water to flow outwardly toward the outer diameter of the bit. Water in the air flow cannot turn up, around and down the air-tubes 7 of the bit. FIGS. 2A and 2B illustrate such an arrangement installed in a bit. As shown in FIG. 1A, the vanes 1 are arranged at a relatively abrupt angle so as to accelerate flow over the vanes 1.
FIG. 3 illustrates another existing solution to separate the water and air in flushing medium. The separator shown in FIG. 3 is inserted in a drill string adjacent a drill bit. The structure shown in FIG. 3 operates by forcing the liquid portion of the flushing medium outwardly through centrifugal force, as indicated by the outward directed arrows. On the other hand, the gaseous portion of the flushing medium flows down through the central passage of the structure. This structure includes large sections that decrease the flow area for the air and liquid.
Existing solutions have a number of associated problems. For example, the blades in a centrifugal force separator cause a sudden acceleration of the air/water flow, which can generate a large back pressure above certain flow volumes of air. Back pressure can be considered as a pressure drop across the device. Many flow components reference pressure drop since a minimum pressure must be maintained. The existing centrifugal air/water separator utilized in a 6⅝″ API connection bit is limited to a flow of about 2700 scfm. This flow rate produces a back pressure of about 20 psi. Backpressure can cause problems with the compressor generating the air flow. As a result, the air flow may need to be reduced below a rate that is functional for the bit.
To help reduce back pressure, open areas 11 were included between the vanes, shown in FIGS. 1B and 2A, to produce an open flow. However, even with the open areas, back pressure is still a problem. Once the open areas are increased enough to adequately lower back pressure the separator no longer provides enough centrifugal force to move the water outward away from the air-tube inlets under the dome.